Given the increasing scarcity of resources and the increased efforts to save energy associated therewith, systems of the type described above are becoming increasingly important. For this reason, such systems are frequently used in hydraulic equipment and systems, in which actuators in the form of working cylinders are provided. In the case of raising and lowering applications, the potential energy of a load that has been lifted can thereby be converted into hydraulic energy by the working cylinder, which energy can be stored and fed back. Such a system can also be used for load compensation.
In the relevant systems of this kind from the prior art, the efficiency of the energy conversion leaves something to be desired. One reason for this problem is the dependency of the charging and discharging processes of the hydraulic accumulator on the respective system pressure. More specifically, the hydraulic accumulator can only be charged when the system pressure is greater than the gas pressure present in the accumulator on the gas side. If the system pressure cannot be established in the respective operating situation of the working cylinder, it will not be possible to acquire energy in the accumulator. The discharging process of the accumulator is thus subject to limitation if energy from the accumulator can only be fed back when the accumulator pressure is greater than the current system pressure. An additional problem is that, in the case of an accumulator pressure that is greater than the current, needed system pressure at the working cylinder, the pressure level of the accumulator and the system needs to be balanced by valves. The energy, which is latent in the differential pressure between the accumulator pressure and the system pressure, is then lost as a result of throttling losses.
DE 100 06 013 A1 discloses a device for saving energy in hydraulically actuated work equipment through the use of a piston accumulator. In the known solution, a fluid control has a control device, by which the piston accumulator can be connected to, or disconnected from, a fluid circuit of the work equipment. The control device has a monitoring device for such switching operations, which monitoring device at least detects system conditions of the work equipment and/or of the piston accumulator. The device for saving energy then is only used when an actuation of the work equipment appears to be necessary during normal operation. Special operations with the machine, in which the work machine is completely unloaded or very heavily loaded, are not hindered. A favorable energy conversion is thereby achieved with the known solution.